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<html lang="en">   
<head>   
  <meta charset="UTF-8">   
  <meta name="viewport" content="width=device-width, initial-scale=1.0">   
  <title>const命令声明常量值</title>   
  <script>   
    const PI = 3.1415926;   
    console.log(PI);    
    PI = 3.14; // Uncaught TypeError: Assignment to constant variable.     
   </script>   
 </head>   
 <body></body>   
 </html>  